This invention relates to a system for detecting defects on an optical surface and, more particularly, to a system for detecting surface defects such as scratches, cracks, pin holes or the like on the optical surface of an object such as a semiconductor wafer or the original disk of an optical video disk on which no information is recorded.
It is generally required that the surface of a semiconductor wafer or of an original disk of an optical video disk on which no information is recorded should be optically flat. Accordingly, the surfaces of these wafers and disks are polished to become optically flat. It is then necessary to inspect whether the surfaces of these wafers and disks are reliably optically flat. In the conventional surface inspection, the surface of an object to be inspected is illuminated, is photographed by a TV pick-up tube or the like, and an enlarged, image is visually inspected by a person to discover any defects.
Since it is necessary to provide a TV camera having a high resolution in the human visual inspection technique, this inspection technique incorporates problems, e.g., personal differences, fatigue and so forth, and a skillful inspector is required. This conventional inspection technique is inefficient, unreliable, and it is difficult to quantify defects. It is also difficult to reliably detect fine surface defects.